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.TH SIGQUEUE 3C "Feb 5, 2008"
.SH NAME
sigqueue \- queue a signal to a process
.SH SYNOPSIS
.LP
.nf
#include <sys/types.h>
#include <signal.h>

\fBint\fR \fBsigqueue\fR(\fBpid_t\fR \fIpid\fR, \fBint\fR \fIsigno\fR, \fBconst union sigval\fR \fIvalue\fR);
.fi

.SH DESCRIPTION
.sp
.LP
The \fBsigqueue()\fR function causes the signal specified by \fIsigno\fR to be
sent with the value specified by \fIvalue\fR to the process specified by
\fIpid\fR. If \fIsigno\fR is 0 (the null signal), error checking is performed
but no signal is actually sent. The null signal can be used to check the
validity of \fIpid\fR.
.sp
.LP
The conditions required for a process to have permission to queue a signal to
another process are the same as for the \fBkill\fR(2) function.
.sp
.LP
The \fBsigqueue()\fR function returns immediately. If \fBSA_SIGINFO\fR is set
for \fIsigno\fR and if the resources were available to queue the signal, the
signal is queued and sent to the receiving process. If \fBSA_SIGINFO\fR is not
set for \fIsigno\fR, then \fIsigno\fR is sent at least once to the receiving
process; it is unspecified whether \fIvalue\fR will be sent to the receiving
process as a result of this call.
.sp
.LP
If the value of \fIpid\fR causes \fIsigno\fR to be generated for the sending
process, and if \fIsigno\fR is not blocked for the calling thread and if no
other thread has \fIsigno\fR unblocked or is waiting in a \fBsigwait\fR(2)
function for \fIsigno\fR, either \fIsigno\fR or at least the pending, unblocked
signal will be delivered to the calling thread before the \fBsigqueue()\fR
function returns. Should any of multiple pending signals in the range
\fBSIGRTMIN\fR to \fBSIGRTMAX\fR be selected for delivery, it will be the
lowest numbered one. The selection order between realtime and non-realtime
signals, or between multiple pending non-realtime signals, is unspecified.
.SH RETURN VALUES
.sp
.LP
Upon successful completion, the specified signal will have been queued, and the
\fBsigqueue()\fR function returns  \fB0\fR. Otherwise, the function returns
\fB\(mi1\fR and sets \fBerrno\fR to indicate the error.
.SH ERRORS
.sp
.LP
The \fBsigqueue()\fR function will fail if:
.sp
.ne 2
.na
\fB\fBEAGAIN\fR \fR
.ad
.RS 11n
No resources are available to queue the signal. The process has already queued
\fBSIGQUEUE_MAX\fR signals that are still pending at the receiver(s), or a
system wide resource limit has been exceeded.
.RE

.sp
.ne 2
.na
\fB\fBEINVAL\fR \fR
.ad
.RS 11n
The value of \fIsigno\fR is an invalid or unsupported signal number.
.RE

.sp
.ne 2
.na
\fB\fBENOSYS\fR \fR
.ad
.RS 11n
The \fBsigqueue()\fR function is not supported by the system.
.RE

.sp
.ne 2
.na
\fB\fBEPERM\fR \fR
.ad
.RS 11n
The process does not have the appropriate privilege to send the signal to the
receiving process.
.RE

.sp
.ne 2
.na
\fB\fBESRCH\fR \fR
.ad
.RS 11n
The process \fIpid\fR does not exist.
.RE

.SH ATTRIBUTES
.sp
.LP
See \fBattributes\fR(7) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Committed
_
MT-Level	Async-Signal-Safe
_
Standard	See \fBstandards\fR(7).
.TE

.SH SEE ALSO
.sp
.LP
.BR kill (2),
.BR sigwaitinfo (3C),
.BR siginfo.h (3HEAD),
.BR signal.h (3HEAD),
.BR attributes (7),
.BR standards (7)
